The All-Star first baseman was in Philadelphia to see the team physician on Tuesday. The second-place Phillies are in Florida for a three-game series with the Marlins.
Howard hurt his left ankle scrambling back to second base during Sunday's game at Washington. He left the ballpark on crutches.
Howard, the 2006 NL MVP, is hitting .292 with 23 home runs and 81 RBIs. The Phillies already are missing All-Star second baseman Chase Utley and center fielder Shane Victorino because of injuries.
Taking Howard's place will be John Mayberry, Jr. from Lehigh Valley.
Mayberry, 26, was hitting .258 (99-for-383) with 12 home runs and 54 RBI in 99 games for Lehigh Valley this season.
Fifteen Phillies have gone on the DL this season.